1. Field of the Invention
The present invention relates to a lens driving device for an auto-focusing camera.
2. Description of the Prior Art
The camera lens driving device of the prior art is exemplified in Japanese Patent Laid-Open No. 62-200339. According to this camera lens driving device, in order that a lens driving member associated with a step motor may be stopped at a focal point, a retaining member for retaining the teeth of a ratchet wheel associated with the lens driving member is caused to retain the teeth of the ratchet wheel, when the step motor rotates to bring the lens driving member to the focal point, by an electromagnet thereby to restrain the lens driving member from further movement.
However, the camera lens driving device of the prior art is troubled by the following problem. Because of the errors of the step angle of the step motor and/or the accumulated errors of the clearance due to the insufficient accuracy in the parts or the assembly of the power train from the step motor through the gear train (e.g., the idler gear), the moving member and the lens driving member to the ratchet wheel, the engagement between the ratchet wheel and the retaining member may not occur at the proper position thereby making the focusing improper.
Therefore, a camera such as a multi-focal lens camera needing many lens stop positions is newly required to have means for stopping the lens driving member accurately in the many lens stop positions. This requirement is difficult to be satisfied within the limited operational space of the lens driving member and may increase the size of the camera.
In order to stop the lens driving member accurately at the focal point, moreover, the clearance has to be reduced by improving the accuracy of the parts of their assembly but this is limited. In accordance with the number of the lens stop positions, still moreover, the ratchet wheel has to be enlarged to raise another problem that the camera is also large-sized.